Sapphire crystal glass is more desirable in the vast majority of cases because of its scratch resistance. True, it may be less shatter resistant than mineral glass, but this is irrelevant unless you plan to drive a car over your watch
Scratch resistance matters though: through day-to-day use you'll probably swipe a wall with your watch or at some point even drop it on the ground.
With a mineral glass you'll get unsightly scratch marks that you'll be reminded of every time you glance at your watch. Sure, you can replace mineral glass if it gets scratched -- and the watch is designed to be repairable -- but it's a pain. If you're investing in a watch, you may well get a good piece of sapphire that solves that problem and looks brand new for years and years.
Sapphire crystal is much more expensive than mineral glass, and brands that are really serious about quality only use sapphire crystal.
In our opinion it’s practically sinful to make watches with cheap mineral glass -- a few dollars extra in production cost makes the difference between a disposable, high-maintenance accessory and one that will look great for decades.
Tip #3: Check the movement
The movement is the engine of the watch that drives the hands around the dial and powers the watch's other functions (e.g. calendar, chronograph function, etc.). But all movements are not made equal. A good movement will keep time reliably; a badly made one will not. This is known as “losing time”, where a watch with a bad movement has tick speeds that are inconsistent. A bad watch can lose minutes a day.
Swiss, Japanese and German movement makers have the best reputations whether it’s for automatic or quartz movements. They lead the industry in innovation. Some of the most well-known Swiss movement makers are Ronda (particularly for quartz movements), ETA and Sellita. In Japan you have Seiko, Miyota and Citizen, etc. There's also a number of independent movement makers, particularly in Germany and Switzerland.
However, as with any "Made in" designation, it's impossible to say, "all movements from [country] are good". Any country has good suppliers, not-so-good suppliers, and downright bad suppliers. Best is to ask who the manufacturer is for the particular model and do some searching for yourself online.